How do you upload family histories?
I guess that mainly depends in what format you now have it. And also depends on WHERE in FamilySearch you are hoping to upload it to.
Are you referring to some printed paper based family report? a book? a digital document?
Your first step is to convert paper or digital into a PDF file format.
THEN - if you are wanting to upload it to FamilySearch Memories - you can use the document upload option.
IF you want to submit it as part of Family Search "Books" see this page:
If you want to contribute a physical book - check out this link:
Here is an examples of Family Histories uploaded as memories items:
Here is an example of a Digital Book entity: